The present invention is directed generally toward coal preparation plants and, more particularly, toward an improved integral dilute media/plant clean-up sump for retaining dilute media and circulating the dilute media for use by the coal preparation plant.
Coal preparation plants separate organic and non-organic solid particles by their specific gravities. The coal preparation plant receives a feed of raw mined coal, and separates the raw mined coal into clean coal and refuse. These plants typically utilize two basic processing methods for separating raw coal from rock and varying proportions of striated rock and coal from the higher quality coal. The two processing methods include heavy media and water based separation methods Heavy media, utilizing a slurry of water and media (magnetite or ferrosilicon) to separate the coal from the refuse according to their specific gravity of dry solids, is the most common separation process for larger size (Plus 1 mm-0.5 mm) particles. Whereas, water based separation processes are more commonly used for the xe2x80x9ccleaningxe2x80x9d of the finer sized particles, as that term is commonly understood in the coal processing art.
The clean coal and refuse from the heavy media type plants are fed to vibratory screens. While on the clean coal and refuse screens, the majority of the recirculating media is recovered in the drain section of the screens. The clean coal and refuse particles are rinsed with water to remove the remaining portion of adhering media. The finer solids particles, media and water passing through the respective screen is defined as dilute media.
The dilute media slurry recovered by the rinse section of the underpans is traditionally piped to a dilute media sump or gravity fed to a magnetic separator. To maintain the required operating specific gravity separation point of the heavy media separation process, a portion, or bleed, of the correct medium slurry recovered by the drain sections is removed from the recirculating medium slurry flow and fed to the dilute media circuit. The dilute media is then pumped from the dilute media sump to a magnetic separator for media recovery. The requirement of having an additional dilute media sump increases the overall size of the plant area, and adds to the cost of building the coal preparation plant.
Additionally, the efficiency of the magnetic separator is directly related to media and/or liquid loading. With gravity fed separators, inconsistent feed volumes can result in poor separator efficiency. When both pump and gravity fed magnetic separators are overloaded with solid media, the excess media is lost to the effluent stream. Such media overloading may occur with increased adjustment in bleed volume to compensate to changes in raw coal characteristics, spillages within the plant when fed with a cleanup sump and after the coal preparation plant has been idled for a period of time allowing the media particles to settle at the bottom of the dilute media sump. Upon plant start-up, a large amount of media may be pumped to the magnetic separator from the dilute media sump, resulting in media being lost due to overloading the magnetic separator.
The present invention is directed toward overcoming one or more of the above-mentioned problems.
In a coal preparation plant which receives a raw coal feed and separates the raw feed into a clean coal and a refuse, an apparatus is provided for use therein. The inventive apparatus includes a sump formed in a floor of the coal preparation plant and configured to receive and retain: (a) dilute media, consisting of finely sized particles of coal and refuse, media particles and water, from an underpan of at least one of a refuse screen and a clean coal screen, and (b) coal, refuse and media particles spilled by coal processing equipment in the coal preparation plant. The inventive apparatus further includes a pump associated with the sump for pumping the dilute media and the spilled coal, refuse and media particles received in the sump as a mixture to a media separating device.
Typically, the sump will be formed at a lowest most point in the coal preparation plant in order to also function as a clean-up sump. A screen may also be provided over the sump to prevent the larger coal and refuse particles spilled by the coal processing equipment from entering the sump and clogging the pump. Generally, the pump will be installed in the sump, with its pump suction submerged in the dilute media mixture retained in the sump.
Preferably, the media includes magnetite used for separating the coal and refuse particles from the raw coal and, accordingly, the media separating device preferably includes a magnetic separator for recovering the magnetite from the dilute media mixture.
In another form, the inventive apparatus further includes a nuclear density gauge measuring the specific gravity of the mixture being pumped to the media separating device. The nuclear density gauge is wired to a control system and a control valve which is configured to add water to the sump controlling the amount of media pumped to the media separating device to prevent overloading of the media separating device.
Water is provided to the sump by a water source connected to the sump via at least one valve. The nuclear density gauge integrated control system adjusts the at least one valve to add water to the sump and/or pump suction to dilute the mixture based upon the measured specific gravity value of the mixture.
In a further form of the inventive apparatus, the dilute media received in the sump includes the slurry from the rinse section of the underpan of the at least one of the refuse screen and the clean coal screen, and a portion of the correct media collected in a drain section of the underpan of the at least one of the refuse screen and the clean coal screen.
A method of retaining dilute media formed as a by-product of the coal/refuse separation process in a coal preparation plant is also provided. The method generally includes the steps of providing a sump in a floor of the coal preparation plant for receiving coal, refuse and media particles spilled by coal processing equipment in the coal preparation plant and dilute media from an underpan of at least one of a refuse screen and a clean coal screen. The dilute media and the spilled coal, refuse and media particles received in the sump as a mixture will be pumped to a media separating device. Preferably, the media includes magnetite, and the media separating device includes a magnetic separator.
In one form, the method further includes the step of controlling the amount of media in the mixture provided to the media separating device. The controlling step may include measuring the specific gravity of the mixture provided to the media separating device, and adding water to the sump to dilute the mixture in response to the measured specific gravity value.
In another form of the inventive method, the mixture in the sump is pumped to the media separating device, via a pump, with the water added to the sump to dilute the mixture being added near the pump suction within the sump.
In a further form of the inventive method, a select portion of the dilute media received in the underpan of the at least one of the refuse screen and the clean coal screen is directed to the sump. This select portion of the dilute media typically includes the dilute media collected in a rinse section of the underpan of the at least one of the refuse screen and the clean coal screen, and a portion of the correct media collected in a drain section of the underpan of the at least one of the refuse screen and the clean coal screen.
Preferably, in order for the sump to also function as a clean-up sump, it is provided at a lowest most point in the coal preparation plant. A screen will typically be provided over the sump to prevent the larger coal and refuse particles spilled by the coal processing equipment from entering the sump and clogging the pump.
It is an object of the present invention to:
remove the need for a dilute media sump in coal preparation plants; and
control the amount of media provided to a media separating device within a coal preparation plant.
Other objects, aspects and advantages of the present invention can be obtained from a study of the specification, the drawings, and the appended claims.